Electrostatic printing tube



Oct. 19, 1965 J. A OGLE ELECTROSTATIC PRINTING TUBE 2 Sheets-Sheet 1 Filed Aug. 14, 1961 INVENTOR. JAMES A. OGLE AGENT United States Patent 3,213,309 ELECTROSTATEC PRINTING TUBE James A; Ogle, Paoli, Pm, assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan Filed Aug. 14, 1961, Ser. No. 131,209 24 (Ilaims. (Cl. 313-73) This invention pertains to electron tube structures, but more specifically to electron beam switching tubes. With still more particularly, it has to do with cathode-ray tubes for use in the art of electrostatic recording or printing, and such as described and claimed in the co-pending application of Robert E. Benn, entitled Electron Tube, Serial No. 131,337, filed August 14, 1961, and assigned to the same assignee as the present invention.

In the electron tube art generally, it has been a problem to pass metallic conductors through the tube envelope with a high degree of reliability. In this art it is usual manufacturing technique to heat the glass of the envelope sufficiently either to permit the wire leads to be forced through the walls of the envelope, or for the glass to flow completely around the wire.

A basic problem in following either of these techniques is the forming of air bubbles in the seal area resulting in a leaky seal. This is a particularly difficult problem when it is necessary to attain a vacuum tight assembly of closely spaced and accurately aligned conductors of small dimension such as in cathode-ray tubes for use as electrostatic print heads, and wherein the present invention, as started above, is especially useful.

In electrostatic printing the speed of recording obtainable by deposition of electric charges upon a chargeretentive medium is very great. It is known how to employ fixed electrodes to which rapidly switched potentials are applied in order to achieve recording upon selected portions of such a medium at speeds greatly in excess of those which are obtainable by the use of mechanically moved electrodes. The requirement for fast switching of potentials applied to a recording electrode system for such operations has led to the use of cathode-ray tubes to perform such switching functions. And with their use has come the above mentioned manufacturing difliculties.

It has been found and published (U.S. Patent 2,918,- 580 to Howell, issued December 22, 1959), that electrostatic recording may be practiced particularly conveniently by the use of electrodes of two different functions in the recording electrode assembly. Specifically, a printing electrode (which may be extended over a considerably greater distance than the resolution limit of the recording system) is furnished, from a low-impedance source, a potential with respect to the uncharged surface of the recording medium which is sufficient to drive charges to the surface of the medium and cause them to be deposited there, but is not sufiicient to produce or initiate in the ambient atmosphere a discharge to provide such charges. In proximity to the printing electrode there are provided one or more initiating or selection electrodes which may be selectively driven by highimpedance sources to potentials sufficiently different from the potential of the printing electrode so that an ionizing discharge through the ambient atmosphere occurs between each initiating electrode thus selected and the printing electrode. Such discharges serve as sources of free charged particles some of which are driven by the potential difference between the printing electrode and the surface of the record medium to be deposited upon the record medium, adjacent to the corresponding discharge. It is evident that it is essential to the successful operation of an electrode system of this type that the spacing between the initiating or selection ice electrodes and the printing electrode be maintained uniform; and that, further, if a convenient form of printing electrode such as a bar is to be utilized, this uniformity of spacing requires that the initiating electrodes be accurately aligned.

A particular advantage of the electrode system hereinafter described, when applied to a cathode-ray switching tube, is that it is only the initiating or selection electrodes which need be driven by such a tube; and, since the occur rence of the discharge from an initiating electrode to the adjacent printing electrode automatically brings the two electrodes within a few hundred volts of each other in potential, the voltage excursion of the initiating electrodes as a result of secondary-emission phenomena is restricted, making the operation of the system less sensitive to different secondary-emission characteristics of various targets.

The sealing of metal electrodes into glass ordinarily requires that the molten glass must wet the metal to produce an hermetic bond, and, in order that this bond be not ruptured or the surrounding glass cracked by differential contraction of the glass and the metal during the cooling of the seal, the metal and the glass must have very nearly identical thermal contraction characteristics.

Cathode-ray tubes are known in which a multiplicity of electrodes are sealed in the face of the tube, extending therethrough to form discharge electrodes at the outer face. Apart from the difficulty of fabrication and the secondary-emission problems mentioned hereinabove, these tubes suffer from the disadvantage that, no matter how closely the electrodes may be spaced or how small their individual dimensions, the resolution of a recording system employing such a tube cannot be less than the spot size of the cathode-ray tube. It is highly desirable that the size and spacing of the beam targets in a cathode-ray switching tube for electrostatic printing be large relative to the size and spacing of the electrodes in the recording electrode assembly proper; this is in order that high resolution of record be obtainable with relatively poorly focussed beams.

The present invention provides an electron beam tube structure particularly useful as a combined cathode-ray tube and recording electrode assembly which is distinguished, inter alia, by the following advantages:

It is readily and inexpensively producible by techniques adapted to automatic mass-production methods;

It permits the use of conventional glasses for sealing purposes, but is relatively insensitive to the thermal contraction of the metal electrode relative to the glass;

It provides electrodes which are well supported against deformation despite their small size;

It assures accurate alignment of the electrodes;

It is well adapted to the use of the electrode system employing separate selection and printing electrodes;

It provides much finer resolution in the recording electrode system than is required of the cathode-ray beam and deflection system;

It permits the inexpensive mass fabrication of individual electrodes.

Briefiy, I provide an electron beam tube with a faceplate which in its preferred form, though not necessarily, is planar on its inner side and of some rigid impermeable electrically insulating material, such as glass, suited for sealing to the tube envelope. On the faceplate I provide one or more thin conductive strips which form electron beam targets and are extended through the bond between the envelope and faceplate to form external electrodes, such as the discharge electrodes in an electrostatic recording electrode system.

The conductive strips are firmly attached to the faceplate, which attachment may be achieved by evaporating metal on glass in vacuo, or electroplating upon an initial conducting layer produced either by evaporation or by treatment with stannous chloride and subsequent heating, or by the pyrolysis of platinum chloride so-called (actually more nearly chloroplatinic acid, although the commercial material widely employed for this purpose is probably somewhat variable in composition), or the fusion of silver into the surface of the glass. Given such a metal coating upon the glass plate, the desired conductor configurations or patterns may be produced by various well-known techniques such as photoetching, mechanical engraving or routing or ruling, or by employment of stencils to limit the initial application of the conductive material. In any event, the thickness of the electrodes is kept sufficiently low that the yielding of the material will permit it to conform by stretching or corn pression to the contraction of the glass base without rupture of the seal between the conductor and the glass. The glass plate is then sealed against the edges of the walls of a tube envelope without a faceplate, the glass and metal combination being so chosen that wetting of the metal by the glass occurs. The resulting tube has as an integral portion of it a firmly supported accurately aligned row of external electrodes.

For better understanding of my invention I have provided figures of drawing, as follows:

FIG. 1 is a perspective view of a tube faceplate covered with a thin layer of metal on one side;

FIG. 2 is a perspective view of the faceplate of FIG. 1 with a resist superimposed upon the metal layer covering to protect from etchant the portions of the metal required to form the conductor pattern;

FIG. 3 is a perspective view of the faceplate of FIG. 2 after etchant has removed the unprotected portions of the metal layer and the resist has been removed;

FIG. 4 is a fragmentary view in section of the end of a tube envelope to which the faceplate of FIG. 3 has been sealed;

FIG. 5 is a sectional view of a cathode-ray tube formed in accordance with the invention;

FIG. 6 is a sectional view taken along the line 66 of FIG. 5;

FIG. 7 is a view similar to FIG. 4 but showing a modified form of construction wherein a plurality of faceplates are used to provide a print head matrix;

FIG. 8 is a sectional view taken along the line 88 of FIG. 7 but with the tube envelope indicated only by a broken line;

FIG. 9 is a view taken along the line 99 of FIG. 8 and showing the print head matrix as it appears on the exterior of the cathode-ray tube; and

FIG. 10 is an elevational view of the inner surface of a modified faceplate.

Now With reference to the details of the various figures of the drawings and first to FIGS. 4, 5, and 6 it is seen that a combined cathode-ray electrostatic recording tube exemplary of the preferred form of the invention, comprises a glass envelope 1%) having a narrow neck end portion 12 and a flared opposite end portion 14. The beam producin apparatus, such as, electron gun 16 of conventional construction is positioned in the neck portion 12. While only one gun is shown in this embodiment it will be understood that the invention contemplates more, if desired.

When necessary, deflection plates 18 are provided adjacent the gun for cooperation with suitable well known circuitry, not shown, to deflect the beam in the manner, and for the purpose described hereinafter.

The terminal end 20 of the flared portion 14- is covered and sealed by means of a faceplate closure member formed by a flat sheet of glass 22 having firmly bonded thereto a plurality of electrically conductive targets or electrodes 24. In this preferred form of the invention, each of these electrodes has substantial width at 26 in the control area 28 of plate 22 but tapers to narrow closely spaced portions 30 where they pass through the seal where the plate is bonded to the envelope, to terminate in similarly closely spaced external electrodes 32 on a tab extension 34 of plate 22.

As seen in FIG. 5 the end 20 of the envelope 10 is of conventional circular shape, but it is to be understood that other shapes may be used if desired, the face sheet 22, of course, preferably being similarly shaped except for the tab extension 34.

A common bar electrode 36 extends transversely across the ends 38 of electrodes 32 and is electrically insulated therefrom by an interposed insulating strip 40, thus to form a printing head for the recording of electric charge patterns upon a charge retentive medium, as fully described in the above reference Howell patent.

The electrode 24 may be provided in any suitable manner, well known printed circuit technique having been used to advantage. In using such a method, a thin layer or coating 42 (FIG. 1) of electrically conductive material, such as copper, is firmly applied to one surface of glass sheet 22 including the tab portion 34. Such a layer may be applied by rendering the glass electrically conductive by coating it with tin chloride, heating it, and then electroplating the copper thereupon. Alternatively, the glass may be coated with copper or silvered by chemical reduction methods, and then plated. All these techniques are well known.

Since the present invention teaches particularly the advantages of using thin conductors securely bonded to the inner surface of the faceplate to simplify the sealing operation of the faceplate 22 to the envelope 10, the coating 42 is quite thin, of the order of one thousandth of an inch. The glass from which faceplate 22 is formed should be of a composition suitable for scaling to the glass of which the cathode-ray tube envelope it is to be made. I c The glass and the conductive material should be such that the glass will, during sealing, wet the conductive electrode material and form an hermetic seal therewith, although, as has been previously stated and will be further discussed, the matching of thermal expansion characteristics between conductor and glass need not be of the same degree of excellence as is required in conventional sealing of thick conductors into glass.

As seen in FIG. 2 the coating 42 has applied thereto a pattern of etohant resist 44 in a pattern like the desired pattern of separated conductors 24- to be formed by etching. The technique of producing such patterns is well known, a standard reference on the subject being Printed Circuit Techniques, Circular 468, of the National Bureau of Standards of the Department of Commerce of the United States of America. Other references are New Advances in Printed Circuits, Miscellaneous Publication 192, also of the National Bureau of Standards; and Printed Circuits, a reprint from Electrical Manufacturing, Gage Publishing Company, 1250 Sixth Avenue, New York City 2 0, New York.

The glass sheet 22 wit-h its electrically conductive coating 42 and resist is subjected to an etchant bath to remove the unwanted exposed copper coating, followed by a solvent bath to remove the resist, resulting in the finished faceplate 22, as seen in FIG. 3.

It may be observed that, as mentioned above, the pattern of conductors represented in this form of the invention, consists of relatively large and widely spaced target areas 26 across the center or diameter area 28 of the face plate 22, terminating in much finer and more closely equally spaced electrodes 32 which extend substantially to the edge of the tab extension 34. Each electrode 32 is connected to one corresponding central portion or target, and is separated from the other electrodes by a small space. It is thus apparent from this figure that if selective connection to electrodes 32 is to be made by directing a beam of electrons from gun 16 at the central target areas 26, a relatively large diameter beam, scanned over a relatively large range, with only moderate accuracy, will sutfice to select individually a single electrode 5 32 without inadvertent selection of adjacent electrodes which are so close to the selected electrode 32 that the relatively large diameter beam, if directed to a selected electrode itself, would inevitably impinge upon adjacent electrodes as well as the selected one.

Sealing of face sheet 22- to the cathode-ray tube envelope 10 may be accomplished by the application of heat sufficient to render the edge portion of the envelope and the edge portion of the sheet sufficiently plastic so that pressing the two together will cause them to join, flowing around the thin extensions 32 of conductors 24. This method of sealing is, of course, merely a part of very well known glass blowing technique. However, a benefit from the use of the very thin conductors is that the differential expansion between the conductor material and the glass of the plate and the envelope is of much less importance than when conventional relatively thick wire leads are employed.

Such a structure in combination with a cathode-ray tube is particularly useful, since it permits the benefits f the high speed switching obtainable from a cathoderay tube to be combined readily and easily with the high recording speed of electrostatic printing. For uniformity of operation of the various electrodes 32 in cooperation with the bar electrode 36, it is requisite that the gaps between each electrode and the bar electrode be as nearly uniform as possible. The present invention is particularly well adapted to secure such a result, since the use of a rigid element 22 to support electrodes 24 which are of extremely uniform thickness, since they are formed from a single sheet of material, renders it easy to secure uniform gaps by simple care in the mounting of the bar electrode.

While an etching process has been described for forming the required electrodes upon faceplate 22, other methods may be employed. For example, the desired electrode pattern may be printed upon the plate 22 with some conductive ceramic paint such as chlorplatinic acid, or silver oxide paint, either of which, when heated, will produce a conductive metallic layer firmly bonded to the glass. Copper or other suitable metal may then be electroplated upon this conductive surface to form the required conductor pattern; or the paint itself may be applied in thickness sufficient to produce a conductive layer which will survive the heating and slight deformation incidental to the sealing process without suffering a break in the conductive path it provides. Alternatively, a continuous metallic coating like 42 of FIG. 1 may be mechanically divided into different conductors by a ruling engine or equivalent device. If it is satisfactory to forego the benefits obtained by the use of target conductors larger and more widely spaced than the corresponding external discharge electrodes, the ruling engine may be applied to the entire coating of a faceplate whose extension will be as wide as the desired deflection of the cathode-ray beam over the interior of the tube face. This technique permits the formation of multiple extremely minutely spaced electrodes.

A still further possible modification of the process described is to etch in the face of plate 22 depressions corresponding to the desired conductor pattern, and then applying conductors either by painting with conductive ceramic paints or by plating as previously described. Such a procedure slightly simplifies the making of the seal to the cathode-ray tube envelope because the conductors so applied may be finished ofi flush with the surface of the plate 22 so that a plane surface is presented, which is somewhat more readily sealed.

Now with reference to FIGS. 7, 8, and 9 illustrating a modified form of the invention, it will be seen that a x 7 print head matrix may be formed in accordance with the invention by providing a plurality of end plates 50A through 50G, each of which carries electrically conductive target elements 52 on its inner face and which extend to an edge 53 of the tab portion 54 in the manner hereinabove described in connection with the preferred embodiment of the invention. Faceplate 59A is solid, but each succeeding plate B through 506 is provided with a successively larger aperture or window 55 to expose the top portions 56 of targets 52 of successive plates, as seen in FIG. 8, to the interior of the tube whereby the cathode-ray may impinge upon the areas 56 thus to energize the initiating electrodes 57 on the tab 54, all as described above in connection with the preferred form of the invention.

The tube envelope 58 is secured to the inner face 60 of plate 56G, as indicated by the broken line 62 in FIG. 8, and in exactly the same manner as hereinabove described in the preferred form. All of the plates 50A to StlG are secured to each other in the same manner, that is, by heating the glass plates sufficiently so that they will bond together to form an integral unit with the target conductors terminating (57) in a plane on the tab portion 54 as clearly shown in FIG. 8, thus to form the print head matrix.

While it is contemplated that the construction as just described may be useful as a print head in electrostatic printing where no bar electrode is required, in this form of the invention it is contemplated, and preferred, that the bar electrode be included. To this end, and prior to welding the plates 50A through 566 into an integral unit, as described above, bar electrodes 64 are positioned across the ends 57 of the initiating print electrodes 52 with an insulating strip 66 therebetween, as previously descrbed above. Upon the applcation of suitable heat and pressure, the glass of the plates 50A through EGG flow around the bar electrodes and the insulator thus to seal them into a solid matrix, as indicated in FIG. 9.

It is realized of course that the print head unit as seen in FIG. 7 may be constructed by other suitable techniques, but it is believed that that shown and described in FIGS. 7 through 9 is typical of the possibilities presented by the invention disclosed.

The concept hereinabove described also lends itself to another advantageous modification as shown in FIG. 10. In this form the faceplate 6% in addition to the terminal tab 62 is provided with an extension or top tab 64 above the tube envelope 65, and upon which is provided a common bias bus 66 to which all of the conductors 68 are connected. Also in this form of the invention the conductors are formed of different conductive materials throughout their length, as described below. The conductors may be formed as described above but it is preferred to form them in grooves '70 provided in the inner surface 72 of the faceplate 6i). The grooves, which of course, are quite shallow, are filled with the different materials flush with the inner surface 72 and so that together they form an integral conductive strip from bus 66 to the printing end '74.

At the printing end, designated by the letter A, where sparking will occur a tungsten metal may be screened into the groove thus to give long wearing qualities to the electrode. In the portions identified by the letter B where the conductor passes through the seal between the tube envelope and faceplate, and where a good hermetic seal is necessary a metal is used which is compatable with the coefiicient of expansion of the glass, such as silver frit. The frit contains a glass having the same coeflicient of expansion as the glass of the tube envelope and faceplate, and sufiicient silver to make it a good conductor. The portions indicated by the letter C can be any suitable metal providing electrical conductivity, as desired, and may comprise a continuation of the same silver frit used in B. At D where the beam strikes the electrode target a carbon compound may be used, for it will give very low secondary-emission. In the upper portion of the conductor a resistor E, which can again be a carbon compound, may be provided. Thus it is seen that this construction provides an electrode which is not possible with Wire.

What is claimed is:

1. An electron beam tube comprising, an envelope of electrically insulating material, means in one portion of said envelope for generating an electron beam and directing it to a target in another portion of said envelope, a substantially flat faceplate of electrically insulating material bonded by its inner substantially fiat face to said envelope at said other portion and sealing said envelope against atmosphere, a thin substantially flat electrically conductive target firmly attached to the inner face of said faceplate and having a portion extending across said faceplate and through the bond between the envelope and faceplate to terminate on an external substantially flat extension of said inner face of said faceplate thus to form an external electrode, a bar electrode secured to said flat extension, and a flat strip of electrically insulating material separating the bar electrode from said external electrode.

2. An electron-beam tube comprising, an envelope of electrically insulating material, means in one portion of said envelope for generating electron beams, a flat faceplate of electrically insulating material bonded by its inner flat surface to said envelope at another portion of said envelope and having an external straight edge, said faceplate sealing said envelope against atmosphere, a plurality of thin flat electrically conductive target strips firmly attached to the inner surface of said faceplate and extending thereacross and through the bond between the tube and faceplate and substantially normal to the wall of the envelope to terminate in a line at said external straight edge of said plate thus to form electrodes at said edge, each said target strip terminating at its inner end in a wide portion in the path of said electron beams and diminishing in width for at least a portion of its length as it extends across said faceplate, and means in said envelope for directing said beams to selected of said target strips.

3. An electron-beam tube comprising, an envelope of electrically insulating material, means in one portion of said envelope for generating electron beams, a fiat faceplate of electrically insulating material bonded by its inner flat surface to said envelope at another portion of said envelope and having an external straight edge, said faceplate sealing said envelope against atmosphere, a plurality of thin fiat electrically conductive target strips firmly attached to the inner surface of said faceplate and extending thereacross and through the bond between the tube and faceplate and substantially normal to the wall of the envelope to terminate in a line at said external straight edge of said plate thus to form electrodes at said edge, and means in said envelope for directing said beams to selected of said target strips, and wherein said external straight edge is provided by a tab portion extending from said faceplate and beyond the exterior of said envelope, and said tab portion has a fiat surface coplanar with the inner flat surface of the faceplate and to which tab portion are bonded said edge electrodes of said target strips.

4. A construction according to claim 3 wherein a bar electrode is secured to said tab portion of said faceplate across the ends of said edge electrodes and spaced therefrom by electrically insulating means.

5. A cathode-ray tube operable as an electrostatic printing head comprising, an elongated envelope of electrically insulating material, means in one end of said envelope for generating a cathode beam and directing it to the opposite end of said envelope, a faceplate provided with a flat inner surface of electrically insulating material and bonded thereby to said opposite end and forming a target area for said beam, said faceplate having substantially the same coemcient of expansion as said envelope and hermetically sealing said envelope against atmosphere, a plurality of thin flat electrically conductive target strips securely fixed to the inner surface of said faceplate and extending across said inner face and through the bond between said envelope and said faceplate to terminate in a line coincident With an edge of said faceplate, thus to provide a row of printing electrodes at said edge.

6. A cathode-ray tube having a central axis and operable as an electrostatic printing head comprising, an elongated envelope of electrically insulating material, means in one end of said envelope for generating a cathode beam and directing it to the opposite end of said envelope, a faceplate of electrically insulating material bonded to said opposite end and having a flat inner surface forming a target area for said beam, said faceplate having substantially the same coefficient of expansion as said envelope and hermetically sealing said tube against atmosphere, a plurality of thin, flat, electrically conductive target strips securely fixed to said flat inner surface of said faceplate and extending across said inner face and through the bond between said envelope and said faceplate and substantially normal to said central axis and to the wall of said envelope to terminate in a line coincident with an edge of said faceplate, thus to provide a row of electrodes at said edge.

*7. A cathode-ray tube according to claim 6 wherein said faceplate includes a tab portion extending from said tube, said tab having a fiat face coplanar with said inner surface and across which said target strips extend, and wherein said faceplate edge is defined by an outer edge of said tab portion.

8. A cathode-ray tube according to claim 7 and further including a common bar electrode adjacent to and extending across the ends of said edge electrodes and means insulating said electrodes one from another.

9. A cathode-ray tube operable as an electrostatic printing head comprising, an elongated glass envelope, means in one end of said envelope for generating a cathode beam and directing it to the opposite end of said envelope, a glass faceplate bonded to and across said opposite end and having a planar inner surface forming a target area for said beam and a tab portion extending outwardly beyond said envelope and terminating in a straight edge, said faceplate having substantially the same coefiicient of expansion as said envelope and hermetically sealing said tube against atmosphere, a plurality of thin electrically conductive target strips securely fixed to the planar inner surface of said faceplate and extending across said inner face through the bond between said envelope and said faceplate, and across said tab to terminate in a line coincident with said straight edge of said tab, said target strips each having a wide portion in the path of said cathode beam and tapering in width as they extend across said inner face of said faceplate, and all cooperating to form a plurality of narrow closely spaced strips where they pass through the bond between the envelope and faceplate and across said tab, thus to provide a row of closely spaced electrodes at said straight edge.

10. A construction according to claim 9 and further including a common bar electrode secured across but electrically insulated from the end of said edge electrodes.

11. A cathode-ray tube according to claim 10 and further including within said tube means for deflecting said cathode beam selectively to impinge upon said targets.

12. An electron tube having a central axis and comprising, an envelope of electrically insulating material, a faceplate of electrically insulating material provided with a planar inner face and bonded thereby to said envelope, a thin fiat electrically conductive strip firmly attached to the inner face of said faceplate and having a coplanar portion extending across said faceplate and through the bond between the envelope and faceplate and normal to said central axis and substantially normal to the wall of said envelope to terminate at an external edge of said faceplate thus to provide an electrode at said edge, a fiat bar electrode secured to said faceplate across and in parallel relation to said terminating portion of said conductive strip, and a fiat strip of electrically insulating material separating the bar electrode from said terminating portion.

13. An electron tube having a central axis and comprising, an envelope of electrically insulating material, a faceplate of electrically insulating material provided with a flat inner face and bonded thereby to said envelope and sealing said envelope against atmosphere, a plurality of thin flat electrically conductive strips firmly bonded to the inner face of said faceplate and extending thereacross and through the bond between the envelope and faceplate and substantially normal to said central axis and to the Wall of said envelope to terminate at an external edge of said plate thus to provide electrodes at said edge, each conductive strip comprising a tapered portion in the interior of the envelope and a substantially straight portion external to the envelope constituting one of said electrodes.

14. A construction according to claim 12 wherein said external edge is provided by a tab portion extending from said faceplate and beyond the exterior of said envelope and having a surface coplanar with said inner face on which is supported said edge electrode and said bar electrode.

15. A unitary structure comprising an evacuated envelope containing an electron gun having a central axis, means for deflecting a beam of electrons emitted from said gun, a multiplicity of target electrodes arranged in successive ranks in the direction of said central axis, and electrically conductive extensions of said electrodes which extend through the said evacuated envelope and terminate in ends which form a planar regular two-dimensional array of electrodes.

16. A unitary structure comprising an evacuated envelope containing an electron gun having a central axis, means for deflecting a beam of electrons emitted from said gun, a multiplicity of flat target electrodes in successive ranks located in the envelope in a position to be impinged directly by said beam of electrons, and electrically conductive flat coplanar extensions of said electrodes which extend through the said evacuated envelope in a direction normal to said central axis and terminate in ends which form a planar regular two-dimensional array of electrodes whose plane is substantially parallel to the central axis of the said electron gun.

17. A unitary structure comprising a cathode-ray switching tube having an evacuated envelope, an electron gun having a central axis, a multiplicity of electron target electrodes arranged in successive ranks in the direction of said central axis and opposed to the electron-emitting portion of the said gun to selectively receive electrons emitted therefrom, and extensions of the said target electrodes extending to the exterior of the said envelope and terminating in ends which form a planar two-dimensional array.

18. A unitary structure comprising a cathode-ray switching tube having an evacuated envelope, an electron gun in one end of said envelope for generating and controllably projecting a deflectible beam of electrons toward the opposite end of the said envelope, and, at the said opposite end, a multiplicity of insulating plates each of which bears upon the surface nearest the said electron gun a number of separate electrodes formed of thin conductive material each of which electrodes extends to an extremity of the said plate which bears the said electrode, the said plates having portions increasing in height in the direction normal to the said electron gun and partially overlapping each other, the said electrodes in each instance extending past the overlapping portion of the next adjacent plate nearer to the said electron gun to expose the said electrodes to impingement of the said beam of electrons, the extremities of the said plates extending to the exterior of the said envelope, the said plates being hermetically sealed to each other and to the said electrodes and to the said envelope to form a vacuum-tight closure of the said envelope, the said electrodes extending to the extremities of the said plates which extend to the exterior of the said envelope to form electrically conductive mutually insulated connections from the exterior of the said envelope to the interior thereof.

19. A cathode-ray switching tube comprising, an electron gun for controllably emitting a deflection beam of electrons, an evacuated envelope surrounding the said gun and having at the end opposed to the said gun a closure comprising a multiplicity of partially overlapping electrically insulating plates of heights which increase successively toward the end of the said envelope remote from the said gun, one extremity of each said plate extending to the exterior of the said envelope, each said plate hearing upon its surface nearest the said electron gun a pattern of thin electrical conductors fixed to the said surface, each said conductor of each said pattern extending to that portion of the plate bearing it which is not overlapped by an adjacent plate and is exposed to the impingement of the said electron beam and further extending to that portion of the plate bearing it which extends to the exterior of the said envelope, the plates and conductors and the remainder of the said envelope being hermetically sealed together to render the said closure vacuum-tight.

20. A switchable electrode assembly for depositing controllable patterns of electric charges upon a charge-retentive medium, comprising a two-dimensional matrix of discharge electrodes of thin electrically conductive material supported by stiff plates of electrically insulating material arranged in a stack, the discharge electrodes and their supporting plates extending away from the said matrix into an evacuated chamber of which the said plates form a closure by hermetic seals between and among the said chamber and the several said plates and the extended parts of the said electrodes, the said chamber containing means for projecting a beam of electrons which may be variously deflected over an area within the said chamber, the said electrodes extending into the said area within which the beam may be deflected, a portion of each said electrode being directly exposed to selective impingement by the said beam of electrons.

21. A switchable electrode assembly as claimed in claim 6, further characterized by the presence of additional electrodes of which each one forms approximately equal gaps between itself and several of the therein said discharge electrodes.

22. A construction according to claim 5 wherein each of said target strips are formed of different conductive materials suitable for its purpose: a material able to withstand continued sparking at its printing end; a material having the same coeflicient of expansion as the glass of the envelope and faceplate where it passes through the bond therebetween, and a low secondary-emission material in the target area of the cathode beam.

23. A construction according to claim 22 and wherein said faceplate is further provided with an electrically conductive bus securely fixed thereto adjacent the edge opposite to that edge on which the printing electrodes terminate, and said electrodes extend across said plate from said terminating edge to said bus.

24. A construction according to claim 23 wherein said target strips include a resistor between the target area and said bus.

References Cited by the Examiner UNITED STATES PATENTS 2,273,793 2/42 Ekstrand 313-89 2,754,445 7/56 Sorg 313291 X 3,041,611 6/62 Moss 346--74 3,110,764 11/63 Barry 1786.6

DAVID J. GALVIN, Primary Examiner.

RALPH G. NILSON, JOHN W. HUCKERT,

Examiners. 

1. AN ELECTRON BEAM TUBE COMPRISING, AN ENVELOPE OF ELECTRICALLY INSULATING MATERIAL, MEANS IN ONE PORTION OF SAID ENVELOPE FOR GENERATING AN ELECTRON BEAM AND DIRECING IT TO A TARGET IN ANOTHER PORTION OF SAID ENVELOPE, A SUBSTANTIALLY FLAT FACEPLATE OF ELECTRICALLY INSULATING MATERIAL BONDED BY ITS INNER SUBSTANTIALLY FLAT FACE TO SAID ENVELOPE AT SAID OTHER PORTION AND SEALING SAID ENVELOPE AGAINST ATMOSPHERE, A THIN SUBSTANTIALLY FLAT ELECTRICALLY CONDUCTIVE TARGET FIRMLY ATTACHED TO THE INNER FACE OF SAID FACEPLATE AND HAVING A PORTION EXTENDING ACROSS SAID FACEPLATE AND THROUGH THE BOND BETWEEN THE ENVELOPE AND FACEPLATE TO TERMINATE ON AN EXTERNAL SUBSTANTIALLY FLAT EXTENSION OF SAID INNER FACE OF SAID FACEPLATE THUS TO FORM AN EXTERNAL ELECTRODE, A BAR ELECTRODE SECURED TO SAID FLAT EXTENSION, AND A FLAT STRIP OF ELECTRICALLY INSULATING MATETRIAL SEPARATING THE BAR ELECTRODE FROM SAID EXTERNAL ELECTRODE. 